1. From the Department of Neurological Surgery (A.M.S., T.B., A.B., P.A.R., S.I.M.), Cleveland Clinic, Cleveland, OH; Cerebrovascular Center, Cleveland Clinic (A.M.S., M.S.H., T.S., F.H., P.A.R., S.I.M.), Cleveland, OH; Division of Neuroradiology (T.S., F.H.), Cleveland Clinic, Cleveland, OH.